Automated HCV Surveillance Shows Promise But Needs Validation

SaTScan, a free spatiotemporal scanning tool, detected a cluster of acute hepatitis C virus (HCV) cases associated with a verified outbreak at a Los Angeles County pain clinic the day after the second outbreak-related case was reported, according to a proof-of-concept (POC) analysis recently published in JMIR Public Health and Surveillance.¹

The findings suggest that automated cluster detection could help health departments identify outbreaks that traditional case investigation may miss.

Challenges in HCV Outbreak Detection Prompt Automated Surveillance Evaluation

Between 55% and 85% of people with acute HCV infection do not clear the virus on their own, but early diagnosis and treatment can prevent progression to chronic HCV and its complications, including hepatocellular carcinoma. Outbreaks typically arise in settings with a high risk of percutaneous exposure, such as among people who inject drugs and in health care facilities.

California, however, identifies outbreaks when local health jurisdictions investigate individual reported cases, a process requiring extensive medical record review, symptom confirmation, and patient and provider interviews. Staffing constraints limit how quickly jurisdictions can identify linked cases. In addition, acute infections are often asymptomatic, which contributes to substantial underreporting. As a result, national estimates suggest that each reported case of acute HCV may represent up to 13.9 actual infections.²

To determine whether automated methods could address this gap, investigators applied SaTScan, spatiotemporal analysis software that the New York City Health Department has used for routine surveillance of 35 reportable conditions since 2014, to statewide reported acute HCV cases.¹ The researchers first ran a retrospective space-time permutation scan on cases reported to the California Department of Public Health (CDPH), with episode dates between January 2022 and December 2023. They then performed a single prospective POC scan using surveillance data from August 2020 through August 2022, simulating routine surveillance on August 28, 2022; cases among people experiencing homelessness were assigned proxy locations based on their reporting jurisdiction.

Model Detects HCV Cluster Linked to LA Pain Clinic Outbreak

A total of 409 acute HCV cases were reported during the study period, but the researchers excluded 173 (42.3%) from prisons, jails, and federal facilities to focus on community transmission. Of the remaining 236 cases, 231 (97.9%) were geocoded and included, 31 (13.4%) of which occurred among people experiencing homelessness; an average of 10 cases were reported statewide each month.

The retrospective scan identified 1 statistically significant cluster comprising 5 cases in Los Angeles County within a 12-mile radius, with episode dates from August 15 to September 18, 2022 (5 observed vs 0.29 expected; P = .02). Two of these cases were linked to an August 2022 outbreak at a pain clinic, which investigators suspected to be caused by a contaminated multidose medication vial, possibly due to reuse of a needle or syringe.³ A third case was later linked to the clinic after the county health department notified 140 patients of possible exposure.¹ However, because the patient had moved out of state, the case was excluded from the analysis.

The prospective scan detected a 3-case cluster associated with the same outbreak; 2 cases were linked to the clinic. The cluster had a recurrence interval of 1.7 years, indicating that an event of this size would be expected to occur by chance approximately once every 1.7 years under the model. The signal exceeded the prespecified detection threshold, which required a recurrence interval of at least 100 days. Notably, Los Angeles County had originally identified the outbreak by comparing the clinic's patient list with laboratory reports, whereas the scan detected it using only routinely reported surveillance data.

The researchers noted that detection performance depended on parameter choices. Switching from weekly to daily case aggregation reduced the recurrence interval to 77 days, below the detection threshold. In addition, restricting the maximum spatial radius to 10 km reduced it to 32 days.

Further Validation Needed

Because only 1 verified community outbreak occurred during the study period, the findings demonstrate feasibility but do not establish the method’s sensitivity, specificity, or timeliness across outbreaks. The prospective scan also used historical data in which most case investigations had already been finalized. In real time, more pending cases could introduce noise and false-positive signals.

Other study limitations include the underreporting and misclassification of acute infections, which may also limit any cluster detection method. The analysis also excluded incarcerated individuals, who have a higher incidence of acute HCV than people in community settings.

Despite these limitations, CDPH plans to run SaTScan automatically each week. Epidemiology staff will review signals and contact local health jurisdictions when clusters exceed the 100-day threshold. The researchers emphasized, however, that further evaluation is needed.

“In practice, effective cluster detection depends on the timeliness and completeness of case reporting, as well as the granularity of the spatial information and the volume of case data available,” the authors wrote. “Future research should evaluate SaTScan in real time to determine whether it consistently detects outbreaks early enough to support timely public health responses.”

References

1. New S, McLean R, Snyder RE, Martínez-López B. Detection of acute hepatitis C outbreaks in California using SaTScan: statewide spatiotemporal analysis. JMIR Public Health Surveill. 2026;12:e104761. doi:10.2196/104761
2. Klevens RM, Liu S, Roberts H, Jiles RB, Holmberg SD. Estimating acute viral hepatitis infections from nationally reported cases. Am J Public Health. 2014;104(3):482-487. doi:10.2105/AJPH.2013.301601
3. Alarcón J, Dao BL, Santos M, et al. Hepatitis C virus outbreak at a pain clinic in Los Angeles. Infect Control Hosp Epidemiol. 2024;45(4):549-550. doi:10.1017/ice.2023.294